In fusion splicing optical fibers using an electric arc generated between electrodes one of the most important parameters to be selected in the best possible way is the electrode current or fusion current passing between the electrodes in the arc. The electrode current must be determined correctly in order to obtain a low loss and high strength of the splice and an accurate estimation of the optical loss in the splice, see the article W. Zheng, "Real time control of arc fusion for optical fiber splicing", IEEE J. of Lightwave Technology, Vol. 11, No. 4, pp. 548-553, April 1993. The fibers obtained from different vendors, fibers manufactured for different purposes such as single-mode or multi-mode fibers, fibers processed using different treatments, such as fibers coated with titanium or carbon, etc., often need different fusion currents. Even for the same type of fiber, the fusion current has to be increased up to 70% when the place where the fusion welding is made varies from 100 m to 5000 m above sea level owing to the difference in the ambient air pressure. Moreover, since after a number of splices the particles evaporated from the silica fibers will gradually be plated on the surface of the electrodes used for the fusion welding, the current should often be readjusted for the changing conditions of the welding electrodes. To find out a suitable fusion current, many different methods have been developed, such as the well-known melt-back method, see G. Kiss, "High yield fusion splicing in the outside plant: using fiber meltback to monitor electrode condition," National Fiber Operation Engineering Conference, Denver, U.S.A., Sept. 1996, methods using barometric sensors, the offset-splicing method, see the Swedish patent No. 9501589-7, "Auto-fusion temperature control with an offset-splicing method for optical fiber splicing", etc.